The use of vinyl acetate/ethylene/N-methylolacrylamide (VAE/NMA) copolymer emulsions for making nonwoven products is a well known practice in the industry. One particular nonwovens application involves industrial and personal wipes. The industry requires that such wipes bonded with VAE/NMA copolymer binders demonstrate the following properties: a soft feel; good dry, wet and solvent tensile strengths; and good absorbency rate. In particular, the wet tensile strength and absorbency properties are the most important consideration. The copolymer binder must show good adhesion to cellulosic fibers and the copolymer emulsion must have good mechanical stability, good viscosity stability and a small mean particle size and broad size distribution.
U.S. Pat. No. 4,332,850 discloses a "cold" (10.degree.-35.degree. C.) initiation polymerization process for making VAE/NMA copolymer emulsions. Runs 1 and 2 of Example 1 show the use of Triton 301 surfactant as the sole emulsifying agent. Triton 301 surfactant is identified as the sodium salt of alkylaryl polyether sulfate.
U.S. Pat. No. 4,449,978 discloses a nonwoven product formed from a nonwoven web of fibers bonded together with a binder comprising a vinyl acetate/ethylene/N-methylolacrylamide/acrylamide copolymer.
U.S. Pat. No. 4,698,384 discloses a copolymer emulsion for bonding nonwoven products comprising an aqueous medium having colloidally dispersed therein a copolymer consisting essentially of vinyl acetate, 5 to 35 wt % ethylene and 2 to 10 wt % of an amide functional crosslinking monomer which can be NMA, the copolymer emulsion prepared in the presence of 0.1 to 1 wt % polyvinyl pyrrolidone, based on vinyl acetate in the copolymer. Such emulsion binder copolymers demonstrated improved solvent resistance. Run A in Example 2 shows the preparation of a VAE/NMA copolymer emulsion using Polystep B-27 surfactant. Of the total vinyl acetate monomer used in the polymerization reaction, 20% was added with the initial charge and, upon initiation, the remaining 80% was added continuously over a four hour period.